Advances in pediatric oncology have provided for a increasingly positive prognosis for childhood leukemia. Initial concern for survival is now being augmented by concern about the neuropsychological sequelae of treatment. The aim of the proposed project is to evaluate the longitudinal effects of prophylactic CNS Therapy, intensive CNS Therapy, and no CNS Therapy (control group for the cancer experience per se) on the neuropsychological status of pediatric oncology patients. A test battery developed by a neuropsychologist expressly for the evaluation, will be administered at diagnosis and at yearly intervals. The neuropsychology battery includes the following measures: intelligence, motor and constructional skills, spatialtactile skills, language ability, memory and learning, and academic achievement. Additional information from 2 CT scans, at the beginning and end of treatment, a parents' behavior checklist, and a teacher's school report will supplement the primary data base. The performance of both Spanish and English speaking patients will be evaluated. Data analysis will test the hypothesis that consistent progressive, patterns of disturbances in the child's neuropsychological functioning are associated with the CNS treatment under investigation. Separate data analysis procedures will provide an estimate of how, when and to what degree a particular child is effected, and the degree to which a particular CNS Therapy may place the child at developmental risk with respect to established norms. This information will not only provide the oncologist with pertinent information, but will enable the patient to be counseled for appropriate academic placement.